Dry powder fire extinguishing composition compatible with mechanical foam and methodof extinguishing fires



United States Patent DRY POWDER FIRE EXTINGUISHING COMPOSI- TION COMPATIBLE WITH MECHANICAL FOAM AND METHOD OF EXTINGUISHING FIRES Walter G. Sylvester, West Caldwell, NJ., assignor to Specialties Development Corporation, Belleville, NJ., a corporation of New Jersey No Drawing. Filed Mar. 11, 1958, Ser. No. 720,525 8 Claims. (Cl. 252-7 The present invention relates to dry powder fire extinguishing compositions which are adapted for expulsion from a fire extinguisher by gas under pressure, and, more particularly, to such a composition which is compatible with mechanical foam in the extinguishment of gasoline fires and the like.

It is known that dry powders consisting essentially of sodium bicarbonate or other similar gas evolving substances, or mixtures thereof are effective in extinguishing gasoline fires and the like in that they check combustion and smother or knock down flames. Such powders, in order to render them non-caking during storage and freefiowing when expelled from the extinguisher or otherwise directed on the fire, have admixed therein between about /2% to about 3%, by weight of the composition, of a finely-divided, water-insoluble metallic salt of a saturated, mono-basic, fatty acid having from 12 to about 18 carbon atoms, such as aluminum, barium, calcium, lead, lithium, magnesium and zinc salts of laun'c, mystic, palrnitic and stearic acid, barium stearate being preferred because of its stability at temperatures between -65" It is also known that gasoline fires or the like can be Lffectively extinguished by the application of mechanical foam thereon, that is, a foam produced by aspirating or heating air into aqueous salt solutions containing a foam tabilizing agent such as oak bark or licorice root extract, roteinaceous material, glue, albumin, casein, glucose, pent sulfite liquor or saponins. Such foam is particuarly efi'ective as a fire extinguishing agent in that it orms an oxygen excluding blanket and acts as a coolant c prevent rekindling or reflash of the fire.

It therefore has been proposed to utilize the comined desirable effects of powder and foam in extinguishg or controlling large gasoline fires such as may occur or adjacent refinery storage tanks or in connection ith crash fires at airports and landing fields. Attempts ave been made to extinguish such fires by applying both fiowder and foam simultaneously or successively thereon, but such attempts have been unsuccessful because the 'powder upon being contacted by gasoline, wetted soaps iuch as heretofore contained in the powder, whereby the wetted soap caused the foam to be disintegrated and break down practically instantly whereupon the blanketing effect of the foam was completely destroyed. Accordingly, the primary object of the present invention is to provide a dry powder fire extinguishing composition which will not break down or disintegrate me- :hanical foam in the extinguishment of gasoline fires or the like, but will tend to stabilize the foam.

Another object is to provide such a powder which is free-flowing and non-caking.

A further object is to provide such powders without substantial increase in cost over various dry powders now :ommercially available.

I Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in Patented Sept. 13, 1960 the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

In accordance with the present invention, it has been found that the foregoing objects can be accomplished by providing a dry powder composition which comprises a finely divided, free-flowing mixture of a major amount of a pyrolytic fire extinguishing gas evolving substance normally having a tendency to cake on standing, and a sufiicient amount of zinc azelate to render the substance non-caking and free-flowing.

The substance generally characterized herein as a fire extinguishing gas evolving substance may be potassium bicarbonate, or sodium bicarbonate, or other compounds having similar properties or mixtures of any of these compounds, such as sequi-carbonates, for example, NaHCO -Na CO -H O, or other complex carbonates such as l.6NaHCO -Na,CO -2H,0.

It is primarily desirable that these substances can be stored in anhydrous form; are pyrolytic, that is, can generate a fire extinguishing gas, such as carbon dioxide, upon decomposition by heat to create an atmosphere effective to check combustion; and can be projected on the fire in the form of a finely divided, dust-like spray forming a cloud of particles cooperating with the gas generated to blanket or smother the fire, and when settling on the seat of the fire, to lower the heat of the burning materials and products of combustion to a value at which combustion will be inhibited.

The use of sodium bicarbonate is preferred because of its comparative cheapness and general availability in large quantities. Hence, tests made in connection with the present invention have been confined to the use of sodium bicarbonate, although the results sought to be demonstrated could have been made with any of the other fire extinguishing gas evolving substances containing zinc azelate.

The zinc azelate serves to lubricate the particles of fire extinguishing gas evolving substance to render the same non-caking, over long periods of storage, and free-flowing, upon being expelled by gaseous pressure or being thrown on a fire by mechanical means.

It has been discovered that zinc azelate has the peculiar properties of not adversely afiectipg mechanical foam when applied to gasoline fires or fires of similar hydrocarbons. To demonstrate this, a quantity of zinc azelate in finely divided form was distributed on the surface of the gasoline, and then a quantity of mechanical foam was sprayed on the surface of the gasoline. The foam, upon coming in contact with the gasoline wetted zinc azelate, did not disintegrate or break down but remained on the gasoline in its frothy state for at least about three minutes, which demonstrated that the foam is capable of blanketing the source of a fire for a sutficient duration to effectively smother the fire and to prevent reflash thereof. Actually, if the foam remains in state several minutes, extinction of the fire would be assured un'der practical conditions of application.

To further demonstrate this unusual property of zinc azelate, to wit, its compatibility with mechanical foam on gasoline, the foam was first applied and the zinc azelate was then sprayed on the foam. Again, the zinc azelate had no effect on the foam.

Other extensive tests were conducted in a similar manner with metallic salts of mono-basic fatty acids, but in each case the mechanical foam broke down practically instantly and lost its blanketing effect. This perhaps should be attributed to the gasoline solubility of such soaps, whereby the resulting soap solution acts as a wetting agent which disperses and breaks the foam emulsion.

The metallic salts of other polybasic fatty acids and other metallic salts of azelaic'acid also were tested in the foregoing manner, but none of these accomplished the results attained by zinc azelate. Certain of these salts failed to afford proper lubrication .for the fire extinguishing gas evolving substances, while others were sufiiciently water soluble to render them ineffective as anti-caking agents.

It thus appears that zinc azelate is compatible with mechanical foam when in contact with gasoline because of its comparative insolubility in gasoline or the like and its low disassociation factor, whereby the fatty acid radicals do not hydralize to break down the foam. Also, zinc azelate has excellent lubricating properties, and is unaffected by the highest temperatures to which the composition would normally be subjected to during storage, e.g. 160 F.

In order to provide a non-caking, free-flowing powder, it has been found that an amount sufficient to attain this effect may be about 1% zince azelate by weight of the powder. However, as a safeguard against prolonged storage of the powder or storage thereof under fiucuating climatic conditions, it appears that between about 2% and about by weight of the zinc azelate would assure noncaking and free-flowing even under the most extreme corditions of storage, between 3% and 4% being preferrcd. Insofar as affecting the mechanical foam is concerned, the quantity of zinc azelate in the powder is immaterial.

The zinc azelate was found to retain its effectiveness to promote flow and to prevent caking while not causing foam breakdown when used in conjunction with known bulking or spacing agents such as corn starch, silica aerogel, mica and tri-ealcium phosphate. About one to about five parts of such agents are admixed with about forty parts of zinc azelate on a weight basis.

A more complete understanding of the present invention in its practical environment will be achieved by reference to the following examples:

Example I About 99 parts by weight pulverized sodium bicarbonate having a particle size in accordance with military specifications, now designated, Mil-F-19S 63 (Aer) July 2, 1956, were thoroughly mixed with about one part by weight of zinc azelate, and about five pounds of such a mixture were placed in a dry powder fire extinguisher of a the type shown in U.S. Patent No. 2,681,707, under dry nitrogen pressure at about 150 pounds per square inch gauge.

A standard gasoline tub fire was started, and was extinguished almost instantly by first blanketing the gasoline at the surface with about four inches mechanical foam and immediately discharging a portion of the contents of the extinguisher thereon. The fire was tested for reignition or reflash, at one minute intervals for three minutes after it had been extinguished, by directing the time of an acetylene torch aerms the blanket of foam.

Example II The same procedure described in the foregoing example was followed, except that about 98 parts by weight of sodium bicarbonate were mixed with about 2 parts by weight of zinc azelate.

Example III The same procedure described in the foregoing example was followed, except that about 97 parts by weight of sodium bicarbonate were mixed with about 3 parts by weight of zinc azelate.

Example IV The same procedure described in the foregoing examples was followed, except that about 96 parts by weight of sodium bicarbonate were mixed with about 4 parts by weight of zinc azelate.

4 Example V The same procedure described in the foregoing examples was followed, except that about parts by weight of sodium bicarbonate were mixed with about 5 parts by weight of zinc azelate.

Example VI The same procedure described in the foregoing example was followed, except that about 98 parts by weight of sodium bicarbonate were mixed with about 2 parts by weight of barium stearate. This test was repeated twice.

The following table contains the results noted in connection with the foregoing examples:

In connection with Examples I to V, it was specifically noted that the appearance of the foam remained unchanged thus accounting for the retention of its blanketing effect for the duration of at least two minutes, whereas in connection with the three runs of Example VI, the foam disintegrated visibly almost instantly thus accounting for the loss of its blanketing effect which enables gasoline vapors to permeate and be reignited.

Another series of tests was conducted in accordance with the foam compatibility fire test-set forth in Mil-F- 19563 (Aer) which requires that a fire extinguished with dry chemical, such as sodium bicarbonate, then reignited and extinguished about 90% with foam, shall not be 100% re-involved in less than two minutes. I

The compositions in accordance with Examples I to V prevented 100% re-involvement for between four and six minutes which demonstrated that these compositions more than comply with the military specification in that respect.

From the foregoing description, it will be seen that the present invention provides a powder compatible with mechanical foam, and an efiicient and reliable method of extinguishing gasoline fires and the like by applying both such powder and foam thereof without danger of reflash or reignition. As indicated by the tests described herein, the powder and foam are compatible regardless of the order in which they are applied to the fire.

It will be understood that the details and examples hereinbefore set forth are illustrative only and that the invention as broadly described and claimed is in no way limited thereby.

I 0 I O l. A dry powder fire extinguishing composition compatible with mechanical foam consisting essentially of a finely divided, free flowing mixture of a pyrolytic fire y extinguishing gas evolving powdered substance and between about 1% and about 5% of zinc azelate by weight of the composition.

2. A dry powder fire extinguishing composition compatible with mechanical foam consisting essentially of a finely divided, free flowing mixture of a pyrolytic fire I extinguishing gas evolving powdered substance and a, sufficient amount of zinc azelate to maintain the sub- I stance free flowing and non-calcing, the zinc azelate being ineffective to break down mechanical foam. 1

3. A dry powder fire extinguishing composition compatible with mechanical foam consisting essentially of a finely divided, free flowing mixture of a pyrolytic fire extinguishing gas evolving powdered substance and at; least 1% of zinc azelate adapted to maintain the sub- I stance free flowing and non-caking, the zinc azelate being ineffective to break down mechanical foam.

4. A dry powder fire extinguishing composition consisting essentially of a flnely divided free flowing mixture of sodium bicarbonate, and about 4% zinc azelate by weight of the composition.

5. The method of extinguishing gasoline fires and the like, which method comprises applying to the fire mechanical foam, and a dry powder fire extinguishing composition consisting essentially of a fine divided, free flowing mixture of a pyrolytic fire extinguishing gas evolving powdered substance and between about 1% and about 5% of zinc azelate by weight of the composition.

6. The method of extinguishing gasoline fires and the like, which method comprises applying to the fire mechanical foam, and a dry powder fire extinguishing composition consisting essentially of a finely divided, free flowing mixture of a pyrolytic fire extinguishing gas evolving powdered substance and a suflicient amount of zince azelate to maintain the substance free flowing and 2 7. The method of extinguishing gasoline fires and the like, which method comprises applying to thefire mechanical foam, and a dry powder fire extinguishing composition consisting essentially of a finely divided. free flowing mixture of a pyrolytic fire extinguishing gas evolving powdered substance and at least 1% of zinc azelate adapted to maintain the substance free flowing and noncaking, the zinc azelate being inefiective to break down the mechanical foam.

8. The method of extinguishing gasoline fires and the like, which method comprises applying to the fire mechanical foam, and a dry powder fire extinguishing composition consisting essentially of a finely divided free flowing mixture of sodium bicarbonate and about 4% zinc azelate by weight of the composition.

References Cited in the file of this patent UNITED STATES PATENTS 2,631,977 Alien Mar. 17, 1953 2,768,952 Anthony Oct. 30, 1956 FOREIGN PATENTS 156,735 Australia May 26, 1954 

8. THE METHOD OF EXTINGUISHING GASOLINE FIRES AND THE LIKE, WHICH METHOD COMPRISES APPLYING TO THE FIRE MECHANICAL FOAM, AND A DRY POWDER FIRE EXTINGUISHING COMPOSITION CONSISTING ESSENTIALLY OF A FINELY DIVIDED FREE FLOWING MIXTURE OF SODIUM BICARBONATE AND ABOUT 4% ZINC AZELATE BY WEIGHT OF THE COMPOSITION. 